Question

A boy of mass 50 kg runs up a staircase of 45 steps in 9s. If the height of each step is 15 cm, find his power. (Take g = 10 ms-2)

Answer 1

Answer:-

Given, mass of body, m = 50 kg

h = 45 x15 = 675 cm = 6.75 m

t = 9 s, g = 10 m

PE = mgh = 50 x 10 x 6.75 = 3375 J

Power of the body = PE / time = Energy / time =

3375 / 9 = 375 W

Answer 2

Answer:

The power is 375 W.

Explanation:

Given,

A boy of mass (m) = 50 kg

No. of steps = n = 45

Time taken (t) = 9 s

Height of each step = 15 cm = 15 / 100 m

To find: find his power

Solution:

Concept involved:  Power is the rate of doing work.

Total height of staircase = No. of steps * height of each step

or, Total height of staircase = 45 * 15 / 100 = 6.75 m

Work done would be equal to the Potential Energy possessed by the body.

i.e W = mgh

here, m = 50 kg , g = 10 m/s^2, h = 6.75 m

Substituting the values,

W = 50*10*6.75

And, Power = work done / time

or, P = W / t

or, P = 50*10*6.75 / 9

or, P = 375 W

Therefore, The power is 375 W.